<html>
    <head>
        <input type="button" onclick="javascript:alert('都说出错了不听？');" value="出错了？点这里">

    </head>
    <body align="center">
        流程控制
    </br>
    </body>
    <script>
        var i = prompt('随便输入字母：','');
        switch(i){
            case 'a' :alert("出错了"); break;
            case 'b' :alert("出错了"); break;
            case 'c' :alert("出错了"); break;
            case 'd' :alert("出错了"); break;
            case 'e' :alert("出错了"); break;
            case 'f' :alert("出错了"); break;
            case 'g' :alert("出错了"); break;
            case 'h' :alert("出错了"); break;
            case 'i' :alert("出错了"); break;
            default : alert("出错了");
            
        }
        

    </script>
</html>